Anti-locking hydraulic brake system comprising a brake force controller

ABSTRACT

Following a general trend, the present invention provides an anti-locking hydraulic brake system to which a brake force controller has been added. However, as opposed to the prior state of art, the brake force controller (21) according to the invention is blocked only once the pump (18) builds up pressure. This means that in any uncritical deceleration, the brake force controller (21) performs its pressure reducing function as soon as the switch-over pressure thereof is attained. This will involve the advantage over other brake force controls actuated only upon failure of the anti-locking function that jamming or seizing of operative elements of the controller is prevented from occurring and that, in addition, a slip control will be required less frequently.

The present invention is concerned with an anti-locking hydraulic brakesystem comprising a brake force controller, of the type as set out inthe preamble portion of the main claim.

A variety of brake systems of the afore-mentioned type are widely knownin the art. For example, DE-37 42 173 describes an anti-locking brakesystem which has mounted in the rear axle brake circuit a brake forcecontroller which, with the aid of an electromagnetic blocking device, isrendered inoperative as long as the anti-locking means is performing itsfunction. However, should a defective condition occur on theanti-locking device, the blocking means would be released, therebycausing the brake force controller to assume its pressure reducingfunction in each decelerating step. This will insure that also uponfailure of the electronic brake pressure control the rear wheels will beprevented from locking before the front wheels in the event of a pedaldeceleration, thereby attaining over brake systems having no brake forcereducer enhanced driving stability in case of a failure of theanti-locking function, involving, however, the disadvantage thatadditional electrical conduits and control signals arerequired to insurethe function of the brake force controller. Moreover, considerationshould be given to the fact that a failure of the anti-locking functionconstitutes an exceptional condition and tha actuation of the brakeforce controller should, if possible, never be needed. If a defectivecondition does occur in years, the brake force controller may becomeunserviceable having got stuck in a blocked position due tocontamination or jamming.

It is, therefore, the object of the present invention to provide a brakesystem of the afore-mentioned type requiring no additional electronicelements for the brake force controller and insuring in case of afailure, through the brake force controller, even after a long-standingservice, a pressure reduction.

This problem, in the practice of the invention, is solved by thecharacterizing features or the main calm. Hence, according to theprinciple underlying the invention the brake force controller starts toperform its pressure reducing function in each uncritical decelerationstep once the switch-over pressure is exceeded, and continues to operateas long as the brake slip values are within the non-critical range.However, once an excessive brake slip is determined causing commencementof the anti-locking function of the brake system the brake forcecontroller, through a blocking device, is rendered inoperative, therebyinitiating the electronically controlled brake pressure control.Actuation ot the blocking device by the pump outlet pressure willeliminate the need to provide an additional electrical feed-in conduitand corresponding electronic signals.

By mounting the brake force controller directly on the wheel brake intothe circuit, a conventional valve block can be readily used withoutrequiring any additional modifications. The brake force controller canbe mounted on the wheel brake.

Assembly will be easier if the brake force control is designed as ascrew-in control involving minor space requirements only.

Additional advantageous features will become manifest from the followingdescription of three drawings, wherein:

FIG. 1 shows a brake system of the invention;

FIG. 2 shows a brake force controller provided for a brake systemaccoruing to the invention;

FIG. 3 shows another form of embodiment of a suitable brake forcecontroller.

The brake system of FIG. 1 operates on the reflux principle. The brakecircuit division is of a diagonal configuration resulting in anidentical design of brake circuits I and II. For this reason, only brakecircuit II is shown herein for purposes of illustration.

In a pedal-actuated deceleration, the main brake conduit 3 ispressurized by the master brake cylinder 1 in communication with thepressure fluid reservoir 2. Such a pressure propagates in the branchbrake conduits 4 and 5 and the supply lines 8 and 9 leading to the wheelbrakes 10 and 11, respectively. Provided in the branch brake conduits 4and 5 are electromagnetically actuated inlet valves 6 and 7 open inde-energized condition. Respectively one outlet conduit 12 and 13 leadsfrom the cross point between the branch brake conduits 4 and 5 and thesupply lines 8 and 9, respectively, to the low-pressure accumulator 16.Located in each of the outlet conduits 12 and 13 is respectively oneelectromagnetically actuated valve 14 and 15 closed in de-energizedcondition. The in-take conduit 17 leads from the low-pressureaccumulator i6 to the in-take side of the pump 18 the pressure side ofwhich, through the pressure conduit 19 and the check valve 20 blockingtoward the pressure side of the pump, is in communication with the mainbrake conduit 3. The wheel brake 11, in the brake system as shown, isassociated to a rear wheel while the wheel brake 10 is part of a frontwheel. For this reason, the brake force controller 21 whose pressurereducing valve is open in deenergized condition and controlled by threepressures is provided in the supply line 9 leading to the wheel brake11. In the opening direction, it is the pressure prevailing on the brakeforce controller which, viewed from the brake force controller, is thepressure on the master cylinder side that becomes effective, while inthe closing direction the pressure on the wheel brake side becomeseffective. Finally, in the opening direction, it is the pressureprevailing in the control conduit 22 that becomes additionallyeffective. That pressure originates from the pressure conduit 19 betweenthe pressure side of the pump 18 and the check valve 20 so that it isalways only the pressure generated by the pump that places the brakeforce controller in its opening position while the control conduit isleft unaffected by the pressure of the master cylinder.

Consequently, the brake force controller 21 operates as follows:

As long as the pump 18 is inoperative, i.e. as long as the brake slipvalues do not exceed a predetermined critical value, the operation ofthe brake force controller 21 corresponds to the one of any conventionalbrake system. If the brake pressure supplied to the wheel brake 11exceeds a predetermined switch-over pressure, the pressure reducingvalve of the brake force controller 21 closes and each additionalpressure increase on the master cylinder side passed to the wheel brakeis reduced. That function is conventional wisdom.

However, once the brake slip on one of the wheel brakes 10 or 11 exceedsa critical threshold Jeopardizig the driving stability, the pump 18starts to operate, delivering from the low-pressure accumulator 16loaded by actuating the outlet valves 14 and 15, respectively. This wayof control is also taught by the state of art. While the pump 18delivers pressure fluid through the pressure conduit 19 to the masterbrake conduit 3 a control pressure is building up in the control conduit22 preventing the brake force controller from carrying out its brakepressure reducing function. The brake pressure control is immediatelyeffected exclusively through the electromagnetically actuated controlvalves, i.e. through the inlet valves 6 and 7 and the outlet valves 14and 15.

Thanks to that circuit configuration the brake force controller 21 isactuated whenever a decalstation step exceeds the switch-over pressureof the brake force controller 21. Jamming of the pistons and otherdefectiveconditions due to a standstill over extended periods of timeare thereby eliminated. Conversely, the anti-.locking function of thebrake system is not needed so frequently as it would be had no brakeforce controller been provided because the brake slip of the rear wheelsis maintained by the brake force controller 21 largely within thepermitted range.

The design of a brake force controller of this type is shown, forexample, by FIGS. 2 and 3.

In the brake force controller as shown in FlG. 2, inlet 30 and outlet 31are arranged in coaxial relationship. The connection for inlet 30 which,in the circuit, is facing the master brake cylinder, is provided with anouter thread. Provided on outlet 31 facing the wheel brake is aninternal thread, thereby preventing a confusion of the two connectionsfrom occurring. Arranged in radial relationship to the axle betweeninlet 30 and outlet 31 is the control connection 32 which is incommunication with the pressure side of the pump, with the casing of thecontroller substantially being formed of three parts. The inlet 30 ismoulded to the casing sleeve 33 whereas the outlet 31 is formed on thecasing body 34. Casing body 34 and casing sleeve 33 are substantially ofa rotation-symmetrical configuration. The control connection 32 isprovided on the connection ring 35 pushed onto the casing body 34.Thehousing body 34 toward the outlet 31 is provided with a positioningaid in the form of a one-step expansions with the casing body 34protruding through the connection 35. The casing sleeve 33 is pushedonto the said end of the casing body 34 protruding through theconnection ring 35 and is in caulked relationship with the casing body34 such that also the connection ring 35 is fixed by the casing sleeve33.

The casing sleeve 33 is provided with an inlet bore 36 extending fromthe inlet 30 into the casing interior in which inlet bore is sealinglyguided the thinner end of a control piston 37. The end of the controlpiston 37 on the inlet side is configured as a valve seat 38, The saidvalve seat 38 cooperates with a valve closing member 39 which isprovided on the inlet side of the control piston 37 and is forced by acentering element 40 to which pressure is applied by a valve spring 41toward the control piston, against plunger 42 passing through the axialbore 43' of the control piston 37.

The inlet bore 36 expands toward a chamber 43 containing no pressurefluid; arranged within the said chamber is a control spring 44 applyingpressure to the control piston 37 through an annular disc 45 in taeopening direction of the valve 38, 39. The thicker end of the controlpiston 37 is sealingly guided within the guiding sleeve 46. The latteris in caulked relationship within the casing sleeve 33. It contains anaxial opening 47 through which plunger 42 protrudes. The end of theplunger 42 protruding through the guiding sleeve 46 is in abutment withthe front side 50 of the blocking piston 48 facing the control piston 37and is moved along therewith. The resting position of the blockingpiston 48 on a step of the casing body 34 on the outlet side isdetermined by the reset spring 49 provided between the guiding sleeve 46and the blocking piston 48. The front sides 50 and 51 of the blockingpiston 48 are interconnected by a passage bore 52. The said passage bore52 is guided in oblique relationship through the blocking piston 48 suchthat it centrally exits out of the blocking piston 48 at the outlet sideyet decentrally terminating on the front side 50 facing the controlpiston, thereby preventing the plunger 42 from passing into the passagebore 52.

The blocking piston 48 is also of a stepped configuration, with themajor and minor circumferences being respectively sealed against thewall of the casing body 34. Provided between the sealants of theblocking piston 48 is the annular control chamber 53 in communicationwith the control connection 32. For that purpose, the control chamber 53is provided with a connecting bore 54 leading to the peripheral annulargroove 55 located circumferentially of the casing member 34 within theaxial section in whichis contained the control connection 32. As theblocking piston 48 has its section of larger diameter on the side of thecontrol piston and its section of smaller diameter on the outlet side, apressure build-up above the control connection 32 exerts a force on theblocking piston 48 toward the control piston. This means that once thecompressire force of the reset spring 49 is exceeded the blocking piston48 is displaced toward the control piston 37 so that the plunger 42displaces the valve closing member 39 toward the inlet 30. With thestroke of the control piston 37 toward the inlet 30 limited through thestep 56 a lock is attained in this way preventing the valve seat 38 fromabutting the valve closure member 39.

Concerning FIG. 2 it should be noted that the positions of the controlpiston 37 and of the blocking piston 48 as shown correspond to adeceleration step in which although the switch-over pressure of thebrake force control is exceeded no brake slip control is performed. Withthe brake not applied, the control piston 37 is moved back to the stopon the guiding sleeve 46. In case of a brake pressure build-up thecontrol piston 37 displaces toward the inlet 30 as the operating face inthe valve closing direction is larger than in the valve openingdirection. Upon commencement of a brake slip control, a control pressureis built up above the control connection 32 thereby displacing theblocking piston 48 toward the control piston 37 so that the valveclosing member 39 is passed to a position outside the range of the valveseat 38.

The principle underlying the brake force controller according to FIG. 3is identical with the one of FIG. 2 except for the coaxial arrangementof the inlet 30 and the control connection 32, while the outlet 31extends in radial relationship to the two other connections. The uppersection of FIG. 3 down to the bottom edge of the control piston 37 isidentical with the one of FIG. 2. The bottom section differs from FIG. 3by the design of the guiding sleeve 46 rigidly secured to the casing, bythe integral formation of the radial connection and the casing body 34,by the arrangement of the reset spring 49 and by the shaping of theblocking piston 48' and 48".

The blocking piston in this case is of a bipartite configuration, withthe blocking piston section 48' facing the control connection 32 beingof a larger diameter than the adjoining blocking piston section 48". Thelatter in this instance is sealingly guided in the extended guidingsleeve 46. The reset spring 49 is arranged within the guiding sleeve 46,supporting itself, with the end on the inlet side, on an internal step57 of the guiding sleeve 46.

The guiding sleeve 46 within its central opening 47 through which theplunger 42 protrudes, includes radial channels 58 interconnecting theinterior of the guiding sleeve 46 with the outlet 31. The annularchamber 59 confined by the thicker blocking piston section 48' on theone hand and by the guiding sleeve 46 with the thinner blocking pistonsection 48" on the other hand, does not contain any pressure fluid andis provided with a radial connection 50 toward the atmosphere which isprotected by the sealing ring 61 against the ingress of dirt.

We claim:
 1. An anti-locking hydraulic brake system, comprising:apedal-operated master brake cylinder in communication with a firstpressure fluid reservoir, a brake conduit leading to at least one brakeof a rear wheel, an outlet conduit leading from the at least one brakeof a rear wheel to a second pressure fluid reservoir, a connectionbetween the brake conduit and the at least one brake of a rear wheel anda connection between the outlet conduit and the at least one brake of arear wheel being made in form of acommomn supply line, a pump fordelivering pressure fluid from the second pressure fluid reservoir intothe brake conduit, an electromagnetically actuated inlet valve providedin the brake conduit, an electromagnetically actuated outlet valveprovided in the outlet conduit, and a brake force controller provided inthe supply line, said brake force controller having an input and anoutput and an only control input and performing a pressure reducingfunction in an inoperative mode of the pump, the pressure reducingfunction of the brake force controller being rendered inoperative bymeans of a blocking device therein when the blocking device ishydraulically actuated through the only control input by the dischargepressure of the pump.
 2. An anti-locking hydraulic brake systemaccording to claim 1, wherein the brake force controller is locatedbetween the wheel brake and the inlet and outlet valves.
 3. Ananti-locking hydraulic brake system according to claim 1 wherein thebrake force controller is of the in-screw type having three pressurefluid connections two of which are in coaxial relationship.
 4. Ananti-locking hydraulic brake system according to claim 1, wherein theblocking device is a blocking piston which moves a valve closing memberand to which the discharge pressure of the pump is applied in theopening direction of the valve, while, in the closing direction of thevalve, the force of a reset spring and the pressure in the wheel brakeare applied thereto.